Oda et al introduced photoacoustic spectroscopy for analyzing particles in water in "Analysis of Turbid Solutions by Laser-Induced Photoacoustic Spectroscopy" in a magazine, Analytical Chemistry, Vol. 52, No. 4, April 1980. It is known, for an analysis of particles in a medium, to apply photoacoustic spectroscopy. In the conventional system, the concentration of the particles has been determined. The capability of measuring the particle size distribution is suggested, but it is not practical yet.